What Causes Palpitations, Headache And Nausea In A Child?

My 14yo daughter has had intermittent episodes of blacked out vision followed by a hot flash. She said the visual change lasts less than 20 sec and always follows with feeling hot, and then symptoms are completely resolved. She has no other symptoms--no dizziness, palpitations, headache, nausea, lightheaded. This has happened with no unusual activity and at rest. She has had migraine headaches in the past and is currently on her period. Your thoughts?